The National Transportation Safety Board was investigating what caused one of Washington's busiest subway stations to fill with smoke Monday afternoon, resulting in the death of 1 person and injuries to 84 others.

Officials said the woman who died and many of the injured were riders aboard a Virginia-bound Yellow Line train that had just departed the L'Enfant Plaza station shortly before 3:30 p.m. local time when it suddenly came to a halt 800 yards beyond the platform and began to fill with smoke.

At a news conference late Monday night, NTSB officials said a so-called "electrical arcing event" occurred approximately 1,100 feet in front of the train. The term refers to what happens when water hits an electrified third rail and sometimes generates smoke. Officials added that there was between half an inch and an inch of water on the ground next to the third rail, but it was not clear why the train came to a sudden stop. 

The smoke did not appear to have been the result of a fire. Power to the third rail was shut down and riders were forced to self-evacuate. Passengers told the Washington Post that as much as an hour went by before firefighters were able to lead them out of the cars. Witnesses told the paper that some riders began to choke as the smoke filled the cars, while others lost consciousness. 

DC Interim Fire Chief Eugene Jones told the Post that firefighters did not immediately enter the tunnel to help the riders because they want to ensure that power to the third rail had been shut off. He also took issue with passengers' claims, saying that the delay was "nothing like" the length of time described. 

NTSB officials said the investigation would continue Tuesday morning. Rail service into the city was expected to be affected. 

At least two of those hospitalized were in critical condition Monday night. 

Jonathan Rogers told The Post that he was aboard a Yellow Line train as it headed to Pentagon Station, which is one station away from L'Enfant Plaza. He said smoke quickly came through the subway car's doors.

"It started to get scary pretty quick," he told the paper. The subway's driver tried moving the train backwards, but smoke continued to enter.

“People started praying,” he said. “Smoke was coming in pretty steadily. Some people were fine and some people were just hurting pretty quickly.”

Passenger Saleh Damiger was quoted by the newspaper as saying that people were choking and yelling aboard the train. "It was a lot of smoke," she said. "We couldn't see each other. ... We felt like we were almost going to die."

Fellow passenger Sirwan Kajjo told the paper that the train operator told them to get low to the ground to avoid being affected by the smoke. 

Eighteen people from the station were taken to Medstar Washington Hospital Center, most of them for smoke inhalation, spokeswoman So Young Pak told the Associated Press. She said 11 were treated and released. Of the seven still in the hospital Monday night, one was in critical condition and one was in serious condition, she said.

George Washington University Hospital spokesman Matt Brock said in an email that 34 patients suffering from smoke inhalation had been brought there. He said their conditions varied.'s Karl de Vries and The Associated Press contributed to this report.

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